Automatic speed control for movie projector

ABSTRACT

An automatic speed control for a sound-synchronized motion picture apparatus. Synchronizing pulses supplied by a tape recorder are compared with pulses generated by the projector. The comparative signal controls a flip-flop which supplies a square wave output signal to a voltage regulator. The square wave controls the voltage regulator which in turn controls the speed of the projector motor. Additionally, the flip-flop output triggers a switching means which shunts a control element of the voltage regulator in the presence of synchronizing pulses from the recorder so as to raise the regulator output voltage during sound-synchronized operation.

United States Patent Bernhold 1 Oct. 24, 1972 [54] AUTOMATIC SPEEDCONTROL FOR MOVIE PROJECTOR Primary ExaminerSamuel S. Matthews AssistantExaminer-Michael L. Gellner [72] Invent Bemhdd wheamn Attorney-WilliamE. Pinsak, John E. Peele, Jr., Ken- [73] g e Bell & Howell p y go, nethw. Greb and William K. Serp Ill.

22] Filed: Dec. 16,1970 [57] ABSTRACT [2]] APPL NOJ 98,504 An automaticspeed control for a sound-synchronized motion picture apparatus.Synchronizing pulses supplied by a tape recorder are compared withpulses [52] US. Cl ..352/17 generated by the projector: h comparativesignal [51] Int. Cl. ..G03b 31/04 controls a flipflop which supplies aSquare wave [58] Field of Search ..352/12, 15, 16, 17; 318/77, putSignal to a voltage regulamn The Square wave 318/314 345 controls thevoltage regulator which in turn controls the speed of the projectormotor. Additionally, the [56] References C'ted flip-flop output triggersa switching means which UNITED STATES PATENTS shunts a control elementof the voltage regulator in the presence of synchronizing pulses fromthe 3,562,615 2/1971 Nasu et al ..318/314 recorder so as to raise theregulator output voltage 3,620,609 I l/ 197] John ..352/22 during soundsynchronized operation 3,266,862 8/1966 Wagoner ..352/15 X 3,588,5586/1971 Levin ..352/l7 X g 4 China, 1 Drawing Figure Patented Oct.24,1972 3,700,315

1:11 [7LU8 T1127?" Edward Burfon Bern/101d AUTOMATIC SPEED CONTROL FORMOVIE PROJECTOR BACKGROUND OF THE INVENTION This invention generallyrelates to an automatic speed control for a movie projector and moreparticularly relates to an automatic speed control for a movie projectoradapted for use with an audio tape recorder providing soundaccompaniment synchronized with the film format.

Various arrangements have been suggested which provided synchronizedfilm accompaniment and motion picture display. One such deviceparticularly adapted for use by the home photographer is described in aUS. Pat. Application by Joseph H. Lancor, Jr., filed Nov. 20, 1967, Ser.No. 684,254, entitled Audio- Visual Recording and Display Methods andApparatus.

As described in the Lancor application, during filming, a tape recorderis connected to and controlled by the camera. Upon energization of thecamera a light within the camera housing is momentarily actuated so asto expose a portion of the margin of the film. Simultaneously with theenergization of the light, the tape recorder is started and the audioaccompaniment is recorded upon one track of a dual track tape. Duringoperation, the camera generates a pulse for each frame advance. Thepulses are recorded upon a second control track of the recorder andserve to hold the recorder and projector in synchronization duringdisplay. Upon release of the camera button, the camera stops and a stopsignal is recorded on the control track of the tape recorder.

During projection, the output of the control track of the recorder isconnected to the projector. The projector motor carries a cam operatedswitch which provides output pulses the rate of which correspond to therate of film movement through the projector. The pulse rate from theprojector is compared with the pulse output of 0 the recorder and theresultant signal is used to control a relay which selectively shunts aresistor in series with the motor and an alternating current therebyvarying the speed of the projector over a limited range.

To facilitate use of the projector for conventional non'sound operation,the series resistance is frequently made variable and adjustable at theprojector control panel. The operator in such an instance manuallyadjusts the resistor and obtain the desired rate of film feed.

When sound operation is desired, this resistance is manually placed atits minimum value so that the projector motor is run in excess of itsdesired speed. This is the maximum speed of the motor and duringsynchronized sound operation the speed is reduced from this value byintermittently inserting the series resistor between the motor and thesupply source. Thus, each time the user operates the projector he mustascertain the position of the control knob set to the resistor shaft.Improper setting will of course, prevent the projector from obtainingsynchronization with the recorder.

It is the main purpose of this invention to provide an improved speedcontrol apparatus for a sound synchronized projector utilizing a directcurrent motor.

Other objects and advantages of this invention will become obvious fromthe following description and drawings in which the single FIGURE is aschematic diagram of a control circuit for a motion picture projectorincluding certain features of this invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT The projector controlapparatus 10, includes a D. C. power source 12, the output of which isconnected to a series voltage regulator 14. The regulator controls thevoltage supply to a projector motor 16 so that the motor speed issynchronized with the speed of a tape recorder 18. Pulse generatingmeans 20 are included which provide a pulse rate related to the speed ofthe projector motor 16. Upon a control track 22 of an audio tape 24 arepulse signals generated by the camera during exposure of the film aspreviously described. The pulse signals of the camera recorded on thecontrol track 22 of the tape 24 are compared with the pulse signalsgenerated by the motor 16 and a resultant signal is generated whichcontrols the operation of the voltage regulator 14. A control circuit 26alternately triggers the regulator into conduction so that the speed ofthe motor 16 is maintained at a speed which synchronizes the pulse ratefrom the audio tape control track with the pulse rate generated by themotor. Serving to efiectively short a portion of the control circuitryof the voltage regulator 14 during synchronized operation is a switchingmeans 28. In the presence of sync pulses from the control track of thetape recorder 24 the switching means 28 serves to short a manuallyadjustable potentiometer 30 of the voltage regulator so as to increasethe regulator output during sound synchronized operation.

More particularly, the D. C. power source 12 includes a transformer 32the primary of which is connected to a commercial power line. Thesecondary of the transformer is rectified by a diode bridge 34, thepositive terminal of which supplies power to the collector of an NPNseries regulating transistor 36. The base of the transistor 36 isconnected to the collector of an NPN control transistor 38 and is biasedby a biasing registor 40 connected between the collector of the controltransistor 38 and the positive terminal of the diode bridge 74. Theemitter of the control transistor 38 is maintained at the desiredpositive voltage reference by means of a reference voltage Zener diode42 connected between the emitter and a ground bus of the diode bridge.Serving to limit the flow of current through the reference Zener 42 is adropping resistor 44 which is connected between the anode of the Zenerand the emitter of the regulating transistor 36.

The output voltage from the voltage regulator is supplied to thevariable speed D. C. motor 16 which drives the projector film and theshuttle mechanism. Bias for the control transistor 38 is obtained bymeans of a resistive network which includes a fixed dropping resistor46, a variable potentiometer 48 which provides course adjustment and afine adjusting potentiometer 50 which is generally made available at thecontrol panel of the projector for convenient use by the operator. Thewiper of the course adjustment potentiometer 48 is connected to the baseof the control transistor 38. As will be hereinafter more clearlydescribed the course adjustment control 48 is set with the fineadjustment potentiometer 50 at its minimum resistive setting to a valuewhich provides regulator output voltage sufficient to drive the motor 16at a speed slightly in excess of that required to maintain synchronizedoperation with the pulse rate on the control track of the recorder 18.The synchronization signals picked up by the control head 52 of the taperecorder are applied through a capacitor 54 to an audio amplifier 56.The positive going portions of the amplified synchronization pulses areapplied through a capacitor 58 and a diode 60 to flip-flop circuit 62.This flip-flop circuit includes two transistors 64 and 66 and isdesigned in a conventional manner so that each pulse passing through thediode 60 opens the transistor 64 which in turn closes the transistor 66.

The transistor 66 is opened in response to the closing of a switch 70which is connected to the base of the transistor 66 through a diode 72.The switch illustrated is a normally open magnetic reed switch, which isperiodically closed by a magnet 74 located on the periphery of a disc76, forming part of the pulse generating means 20. Thus, the disc 76 ismechanically driven by the motor 16 so that the switch is closed onceduring each revolution of the disc. The disc 76 may be rotated by ashaft of the projector which revolves normally at the same rate as theshaft which drives the cam of the camera. Thus, the transistor 66conducts in response to each synchronization pulse derived from the tapeand opens in response to each pulse produced by a closing of the switch70. The angular position of the magnet on the disc is such that theswitch contact is closed during one-half of each frame and is openduring the remaining half of the image frame if the advance of the filmis in synchronization with the movement of the tape.

Thecollector of the transistor 66 is coupled through a couplingcapacitor 77 to the base of a shunting transistor 78 and to theswitching means 28. Providing a ground return for the pulse coupledthrough the capacitor 77 is a diode 79. It will be appreciated that ifthe pulses from the recorder are in synchronization with the pulsesgenerated by the motor the transistor 66 will be conducting an equalportion of the time, generating a symmetrical square wave as at 80.However, if the projector motor speed increases, increasing the pulsefrequency from the generating means as compared to the pulses providedby the recorder 18, the positive going portion of the square wave at thecollector of transistor 66 will narrow and the transistor will beconducting a proportionately shorter period of time. Under suchconditions the square wave will become non-symmetrical with the positivegoing portion being of a shorter duration than the off portion.Conversely, if the pulse rate generated by the projector is less thanthe recorder pulse rate the transistor 66 will remain conducting for agreater portion of time and the positive going portion of the squarewave coupled through the capacitor 77 will be greater than the negativegoing or open condition of the transistor.

The square wave output from the transistor is supplied to the base ofthe shunting transistor 78 through series resistor 82 and the base isbiased to ground by a biasing resistor 84. The emitter of the transistor.78 is grounded and the collector is connected to the anode of the Zenerdiode 42. During the open condition to the switch the shunt transistor78 is non-conducting and the voltage regulating circuit functions in anormal fashion with the Zener diode 42 providing a reference voltage.During the positive going portion of the square wave which correspondsto cutoff of the transistor 66, the shunting transistor 78 is biasedinto conduction creating a short across the Zener diode 72, whichsubstantially places the emitter of the control transistor 38 at groundpotential. Thus, the regulating transistor is switched off dropping thevoltage to the motor. The open period of the transistor 66 determinesthe portion of time which voltage is applied to the motor 16 and thuscontrols the motor speed so as to maintain synchronization with thepulses recorded upon the control track of the tape recorder.

The square wave is coupled through a series RC coupling network 86comprising a capacitor 88 and a resistor 90. The network 86 feeds avoltage doubling circuit 92 including diodes 94, 95. The output of thevoltage doubling circuit is connected to the base of a switchingtransistor 96 and the emitter of the switching transistor is connectedto ground. A parallel RC integrating circuit 98 is connected between thebase and the emitter of the switching transistor 96. The collector ofthe switching transistor is connected to the fixed positive terminal ofthe fine adjustment potentiometer 50. During each positive cycle of thesquare wave, a pulse is supplied to the voltage doubling circuit 92which accumulates in the RC integrating circuit 98 biasing thetransistor 96 to saturation. In this manner, the terminals of thepotentiometer 50 are effectively shorted substantially removing thepotentiometer from the circuit. This operation is obtained withoutrequiring any specific action of the user. Thus, when the projector isoperated with sound synchronization the maximum speed of the motor isautomatically determined by the setting of the course speedpotentiometer 48.

During conventional non-sound operation, the recorder 18 is turnedofiand the input pulses from the control track 24 of the tape arenon-existent. In this condition, the transistor 66 is open, the Zenershunting transistor 78 is thus biased off and the charge upon the baseof the switching transistor 96 bleeds off through a resistor 100 whichforms part of the RC integrating circuit 98. The shunt transistor 78 isalso turned off. The operator may then adjust the projector for thedesired speed by varying the panel knob of the potentiometer 50 in thenormal fashion.

During manufacture, the course adjustment potentiometer 48 which ispreferably located within the projector housing is set, with the finespeed adjustment at minimum resistance, to a value which causes themotor 16 to be driven at a speed in excess of that required forsynchronized sound operation. During non-sound operation, the finepotentiometer 50 is manually adjusted by the user until the projector isoperating at the desired speed. In the event sound accompaniment isdesired, the appropriate audio tape is inserted into the recorder andsynchronization pulses on the control track are fed to the flip-flopmultivibrator causing the relay 68 to alternately open and close. Thesquare wave from the relay is fed to the integrating circuit 98 and thebias developed switches the transistor into conduction providing aneffective short across the fine potentiometer 50. Thus, the operator mayconveniently shift from sound synchronized to conventional projectionwithout the necessity of readjusting the fine speed potentiometer 50.

Although one embodiment of this invention has been shown and described,it is apparent that various changes and modifications may be made, andit is intended in the following claims to cover all such modificationsand changes as may fall within the spirit and scope of this invention.

What is claimed is:

1. A control apparatus for synchronizing a tape recorder providingsynchronizing signals with a motion picture projector motor driving asignal generator which provides an output signal related to the speed ofthe projector motor, a power source supplying power to the motor, avoltage regulator for regulating the power applied to said motor forcontrolling the speed thereof and a comparator controlling the regulatorand serving to compare the synchronizing signal from the recorder withsynchronization pulses supplied by the tape recorder, the improvementcomprising:

switching means responsive to the synchronization pulses from said taperecorder, said switching means being connected to the voltage regulatorand serving to automatically switch the output from the voltageregulator between a first value and a second manually adjustable valuelower than said first value in response to the absence ofsynchronization pulses from the recorder, said voltage regulatorincluding means for manually adjusting said second value said switchingmeans including a switching element connected across said manualadjusting means, said switching means further including means sensingthe presence of the synchronization pulses recorded upon the tape, saidsensing means controlling the operation of said switching means so as toefiectively remove said manual adjusting means from the regulatorcircuit in the presence of the synchronization pulses from the taperecorder.

2. The apparatus of claim 1 wherein said switching means includes atransistor connected across said manual adjusting means and furtherincluding an integrating RC parallel network for storing bias voltage asdetermined by the synchronization signal provided by the tape recorder.

3. The apparatus of claim 2 wherein said comparator includes a relayproviding square wave output signal and said switching means including arectifier connected to the output of said relay and said integratingnetwork and serving to rectify the square wave output of said rectifier.

4. The apparatus of claim 2 wherein said switching means includes arectifier for rectifying the voltage received by said integratingcircuit.

1. A control apparatus for synchronizing a tape recorder providingsynchronizing signals with a motion picture projector motor driving asignal generator which provides an output signal related to the speed ofthe projector motor, a power source supplying power to the motor, avoltage regulator for regulating the power applied to said motor forcontrolling the speed thereof and a comparator controlling the regulatorand serving to compare the synchronizing signal from the recorder withsynchronization pulses supplied by the tape recorder, the improvementcomprising: switching means responsive to the synchronization pulsesfrom said tape recorder, said switching means being connected to thevoltage regulator and serving to automatically switch the output fromthe voltage regulator between a first value and a second manuallyadjustable value lower than said first value in response to the absenceof synchroniZation pulses from the recorder, said voltage regulatorincluding means for manually adjusting said second value said switchingmeans including a switching element connected across said manualadjusting means, said switching means further including means sensingthe presence of the synchronization pulses recorded upon the tape, saidsensing means controlling the operation of said switching means so as toeffectively remove said manual adjusting means from the regulatorcircuit in the presence of the synchronization pulses from the taperecorder.
 2. The apparatus of claim 1 wherein said switching meansincludes a transistor connected across said manual adjusting means andfurther including an integrating RC parallel network for storing biasvoltage as determined by the synchronization signal provided by the taperecorder.
 3. The apparatus of claim 2 wherein said comparator includes arelay providing square wave output signal and said switching meansincluding a rectifier connected to the output of said relay and saidintegrating network and serving to rectify the square wave output ofsaid rectifier.
 4. The apparatus of claim 2 wherein said switching meansincludes a rectifier for rectifying the voltage received by saidintegrating circuit.